Table 3. Results From the Principal Stratification Model of Section 5.3 on Exchanging Needles at the NEP and on HIV Seroconversion.

Estimand	Estimate	95% CR b
(a) Odds ratio of higher versus lower   principal stratumaS for 1 standard   deviation increase in baseline risk   score B: $\exp \left({\beta }_{\left(b\right)}^{\left(S\right)}\right)$	1.15	(1.11, 1.20)
(b) Odds of HIV seroconversion under   fixed exchange for higher versus   lower principal stratumaS, given fixed   baseline risk score B: $\exp \left({\beta }_{\left(s\right)}^{\left(Y\right)}\right)$	2.92	(.99, 96.36)
(c) Odds ratio of HIV seroconversion   for close versus far distance from   the NEP and attributable to needle   exchangec: $\exp \left({\beta }_{(s,d)}^{\left(Y\right)}\right)$	.11	(.0003, 2.23)

^aA subject’s principal stratum is the closest distance to place the NEP beyond which that subject would not exchange at it.

^bJoint confidence region.

^cConditionally on baseline risk score B and principal stratum S.